On 2015/9/8 17:36, Andrey Ryabinin wrote:
> 2015-09-08 4:42 GMT+03:00 Xishi Qiu <qiuxishi@xxxxxxxxxx>:
>> The shadow which correspond 16 bytes may span 2 or 3 bytes. If shadow
>> only take 2 bytes, we can return in "if (likely(!last_byte)) ...", but
>> it calculates wrong, so fix it.
>>
>
> Please, be more specific. Describe what is wrong with the current code and why,
> what's the effect of this bug and how you fixed it.
>
>
If the 16 bytes memory is aligned on 8, then the shadow takes only 2 bytes.
So we check "shadow_first_bytes" is enough, and need not to call "memory_is_poisoned_1(addr + 15);".
The code "if (likely(IS_ALIGNED(addr, 8)))" is wrong judgement.
e.g. addr=0, so last_byte = 15 & KASAN_SHADOW_MASK = 7, then the code will
continue to call "return memory_is_poisoned_1(addr + 15);"
Thanks,
Xishi Qiu
>> Signed-off-by: Xishi Qiu <qiuxishi@xxxxxxxxxx>
>> ---
>> mm/kasan/kasan.c | 3 +--
>> 1 files changed, 1 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
>> index 7b28e9c..8da2114 100644
>> --- a/mm/kasan/kasan.c
>> +++ b/mm/kasan/kasan.c
>> @@ -135,12 +135,11 @@ static __always_inline bool memory_is_poisoned_16(unsigned long addr)
>>
>> if (unlikely(*shadow_addr)) {
>> u16 shadow_first_bytes = *(u16 *)shadow_addr;
>> - s8 last_byte = (addr + 15) & KASAN_SHADOW_MASK;
>>
>> if (unlikely(shadow_first_bytes))
>> return true;
>>
>> - if (likely(!last_byte))
>> + if (likely(IS_ALIGNED(addr, 8)))
>> return false;
>>
>> return memory_is_poisoned_1(addr + 15);
>> --
>> 1.7.1
>>
>>
>
> .
>
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